Zaghari-Ratcliffe was taken to the prison clinic after a blackout on Tuesday, he said. Fellow prisoners called the family saying they were worried about Zaghari-Ratcliffe's condition, he added.

British Foreign Secretary Jeremy Hunt tweeted his support for Zaghari-Ratcliffe, writing: "All our thoughts and prayers with Nazanin and her family today. Unbearable suffering to be apart from daughter with her hopes raised then dashed. We must redouble efforts to find a way to get her home #FreeNazanin."

Zaghari-Ratcliffe was first detained at Tehran's airport in April 2016 while on her way back to the UK from visiting family with her daughter Gabriella, who was then 22 months old.

The Iranian government accused her of working with organizations allegedly attempting to overthrow the regime. She was sentenced to five years in jail and her child was placed in the care of her parents.

Her employer, the Thomson Reuters Foundation, rejected the allegations. In May, Iranian media reported that she was due to face a new trial for "security-related" charges.